When the Seattle Art Museum reopens Saturday, it will be with 70 percent more exhibition space and the potential to continue growing eight floors into the future. It also will reopen as a new institution, a museum whose gaps are not as notable as its depths and cross-cultural connections.

In sharp contrast to the museum's original downtown building designed by Robert Venturi, Brad Cloepfil's silver-blue high-rise expansion is sleekly corporate. Inside, however, old and new spaces flow together with a sweeping sense of air and light. All that, plus restrooms on every floor.

There are three points of entry, all of which take visitors into two floors of the free zone. Besides being full of art, the free zone offers a non-fatally hip museum store and a real restaurant, as well as lecture hall, auditorium and art studio.

On the third floor south galleries are Native arts, Australian and Oceanic, pan-cultural textiles, Asian and American art. In the third floor north galleries are modern and contemporary art from around the world.

The fourth floor south galleries are devoted to traveling and special exhibitions. In the north are ancient Mediterranean and Islamic art, African and European.

In spite of the attempt to blend north and south galleries, there's a striking difference between them. The art provides whatever warmth Cloepfil's north galleries have. While Venturi's south galleries are an embrace, Cloepfil's are cold and anonymous.

In March, after the museum announced nearly 1,000 gifts to its collections valued at more than $1 billion, director Mimi Gates said, "We are now a major museum. We were important before, but now, unquestionably, we are major."

Asked later to expand on that idea, Gates said, "I was speaking not only of the depth, breadth and quality of the collections that were enhanced by the recent gifts, but our new museum with its potential for expansion, the Olympic Sculpture Park and the Asian Art Museum in Volunteer Park. Put them together, and we are a distinctive and nimble museum, major by any standard."

"No other museum is looking as opportunistically at its potential for serving its city as (SAM) is, taking three different forms in three different locations, reshaping itself when the chance arises. In expanding downtown, you are bucking the current fashion for extroverted, look-at-me architecture and turning to an older and stronger tradition of putting function first. It is not a showpiece that Brad Cloepfil is designing, it is a showplace which respects the scale and spirit of its surroundings."

In other words, in an age of feverishly hot museum architecture, the Seattle Art Museum swallowed a chill pill.

Not that it had much choice. Once it agreed to share its downtown block with Washington Mutual, in effect wrapping itself around a bank to make its expansion financially feasible, the museum's construction options narrowed.

Lie down with a bank, get up with pinstripes; but riffing off a bare-bones bank was not the only challenge. Venturi's 1991 building is a faux art deco merger of a traditional Chinese palace and a McDonald's drive-through, five stories of muted razzle-dazzle.

Portland architect Cloepfil was charged with creating a plausible link between art and banking. What he came up with would be a handsome addition to any post-industrial urban core. It's cleaner and more alluring than the bank but doesn't attempt to compete with Venturi's postmodern patchwork.

At 16 stories, Cloepfil's addition is more than three times larger than Venturi's original, and yet Cloepfil's work recedes as Venturi's advances.

Cloepfil's dare-to-be-dull exterior leaves an underwhelming first impression. Yet as a kind of call-and-response pattern, his answer to Venturi makes unconventional sense, reaching around Venturi's postmodernism for a contemporary view of uncluttered, modernist form. I suspect Cloepfil's vertical patterning will wear well over time: baby blue when the sun shines and burnished silver in the rain.

Nothing about the new museum could have been foreseen by SAM founder and first director Richard E. Fuller, who 75 years ago wanted to share his exquisite snuff bottles, Chinese jades and Asian sculptures with the community.

To relieve a blank look at the opening in Volunteer Park, he hung framed reproductions of European art. They remained part of the museum's collection into the 1950s.

Under Fuller's leadership, SAM acquired genuine depth in Asian art, the core of its identity until the mid-1970s.

Modern and contemporary art became important to the museum at that point, when the first modern/contemporary curator was hired. European decorative arts grew next, followed by African and, after the museum opened downtown in 1991, Northwest Coast native peoples.

Successful art museums both respond to and shape the interests of its audiences. By the time SAM aspired to be a generalist museum, capable of surveying a range of world cultures, the European end of the story was out of reach. Also out of reach was American art from the 18th through the early 20th centuries.

African art curator Pam McClusky noted that it was the first American art museum to open with African and art of the Americas getting as much space and attention as European and Asian.

SAM also led in denying the distinction between decorative and fine art. Said decorative art curator Julie Emerson, "We are escaping the bonds of 19th-century European prejudice, which segregated craft from fine art."

Instead, SAM reveled in its strong African and Asian holdings, its new power in art of the Americas and Post-World War II contemporary, and told the story of European art with a smattering of paintings and sculptures connected with a rich, decorative art thread.

That was the pitch in 1991, but it's not the pitch now.

The new SAM remains true to its welcome-to-world-cultures mission, but it is busy filling in the blank spaces on its art map with first-rate acquisitions in American art, European historical and early modernist, especially American modernist. Also for the first time, it can present a credible history of Northwest art, from the 1930s onward.

In the new galleries, decorative art no longer has to carry the narrative thread of the European story. Instead, decorative art gathers force in its own company, linked across time and cultures to dazzle with embellished functionality.

The modern and contemporary galleries are, as expected, brilliant, and the European historical galleries are full of revelations, with new acquisitions and loans.

SAM's higher levels of ambition reflect the rising ambitions of the city, thanks to the range and quality of the art coming into it through private collectors, many of whom have promised those collections to SAM or might well do so in the future.

A decade ago, nobody at SAM would have suggested the museum might one day house a decent grouping of impressionist and post-impressionist art, but Gates says she'd like to try.

"It's our most significant gap," she said. Within the coming decade, that gap could begin to close.